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Transposable genetic elements, spontaneous mutations and the doubling-dose method of radiation genetic risk evaluation in man.

The principal aspects of the 'doubling-dose method' currently used by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the Committee on the Biological Effects of Ionizing Radiation (BEIR) of the U.S. National Academy of Sciences, for the evaluation of genetic radiation hazards in man are briefly reviewed. With this method, which is primarily applicable to autosomal dominant and X-linked disorders, the expected increase in risk from radiation is expressed as a fraction of the current prevalence of these disorders, and thus in relation to an understandable frame of reference. Since the doubling dose is estimated as a ratio of spontaneous to induction rates of mutations, its magnitude is susceptible to changes in either the numerator (spontaneous rate) or the denominator (induction rate). Studies during the past 20 years or so with a number of experimental systems have demonstrated the existence of mobile DNA sequences in the genome and their causal role in the origin of spontaneous mutations, although the proportion of the latter among all spontaneous mutations is not known for any species. If a major proportion of spontaneous mutations in man is mediated by these mobile DNA sequences, and if their mobility is unaltered by radiation exposures, the calculation of the doubling dose in the manner mentioned above, and its use in risk evaluations becomes questionable. However, considerations based on the organization of the human genome would suggest that it is unlikely that a major fraction of spontaneous mutations that lead to disease states in man is due to mobile genetic elements. Consequently, the use of the doubling-dose method for the evaluation of genetic radiation hazards in man would appear to be valid at the present time.

Animals↗

Estimation of the effects of chemical mutagens: lessons from radiation genetics.

Years of work with ionizing radiations have given us a wealth of data on radiation-induced mutations. These data, which have given insights regarding the mutational processes, should form the background for all mutagenesis work. In chemical mutagenesis, as in radiation mutagenesis, it is important to know the shape of the dose-effect curve in order to make further interpretations and calculations. It is also important to be on the constant alert for new relations that can be explored.

Animals↗

Somatic and genetic radiation exposure of the patient in digital subtraction angiography (DSA)

The somatic and genetic radiation exposure of patients undergoing Digital Subtraction Angiography (DSA) and traditional Film Arteriography (FA) of cranial, cervical, thoracic and abdominal vascular territories are compared. The radiation doses absorbed within the critical organs--red bone marrow, lung, thyroid gland and female breast--and in the gonads were measured using an anthropomorphic Alderson phantom. A Somatic Dose Index was calculated in order to estimate the somatic radiation risk. The somatic radiation exposure depends upon the location of the critical organs with respect to the entrance site of the x-ray beam, and can be reduced by an appropriate choice of the angiographic projection. Under this condition, the radiation exposure of the patient during DSA can be lower than during FA. For renal DSA an a.p. projection, the use of an abdominal compression device and careful caudal shielding of the field are advocated.

Cerebrovascular Disorders↗